Date: Thu, 11 Sep 2003 00:10:05 -0700 From: Aaron <[EMAIL PROTECTED]>
At 23:34 -0400 2003/09/10, [EMAIL PROTECTED] wrote:For the /200 case, the processor is run at 200 MHz and the bus is run at 50 MHz (full speed), using a 4 multiplier ... 6 with respect to the PCI cards, which are run at 33.33 MHz (also full speed).
For the /180 case, the processor is run at 180 MHz and the bus is run at 45 MHz, using a 4 multiplier ... 5.5 with respect to the PCI cards, which are run at 32.72 MHz.
The processor, cache, bus and PCI cards must always be run at an integral or half-integral multilier of each other.
I think Peter meand that each bus must be run at an inverse integral or half-integral multiple of the processor speed. The system bus and PCI bus speeds that you give for the 180 MHz processor have a ratio of 5.5:4, or 1.375:1, which is not integral of half-integral.
I missed the earlier messages in this thread, but if the topic is the x500 and x600 machines, the PCI bus speed ratio is completely irrelevant. There is no restriction on the whole-numberedness of the ratio of PCI bus speed to system bus speed.
The PCI bus on the x500 and x600 machines is nailed to the ground. Which is to say, it is run by a 33.3333 MHz oscillator on the motherboard, which isn't going to change it's speed unless you rip it up and physically replace it.
The CPU card can do whatever it wishes with the system bus, the PCI bus stays at 33.3333 MHz no matter what, on those machines. This is also true for the 7200.
The discussion of system bus to CPU speed ratios is correct.
Now this confusion probably arose because on later machines, the PCI bus is related to the system bus by a limited choice of ratios. That is because on later machines a single chip controls the memory bus and the PCI bus and it also creates and buffers the clocks for them. The first machine on which this was true was the Beige G3 which came right after the x600 machines.
But on the x600 and earlier machines, the PCI bus speed is unrelated to the system bus speed--daily dose of mostly useless trivia...
Jeff Walther
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